The proposed studies aim to dissect, understand and influence the function and apparent role of mitochondria, the cell's second genetic system, in oncogenic virus-induced malignancy. In these continuing studies, an ideally controlled cell system of chick embryo fibroblasts infected by wild-type viruses and temperature-sensitive mutants of Rous sarcoma viruses will be employed, in addition to various control, transformed and drug-resistant hamster cell lines. Restriction cleavage maps of mtDNA's, using six restriction endonucleases, will be completed for these cell lines, and the isolated specific segments will be used for hybridization with various RNA species. The previously discovered stimulation of mtDNA synthesis in RSV-transformed chick embryo fibroblasts will be further analysed by purification of mtDNA polymerase(s) and characterization of template specificity and products. MtDNA replicative intermediates and methylation will also be studied. BIBLIOGRAPHIC REFERENCES: M.A. D'Agostino and M.M.K. Nass, 1976. Specific changes in the synthesis of mitochondrial DNA in chick embryo fibroblasts transformed by Rous sarcoma viruses. J. Cell Biol., in press. M.M.K. Nass, 1976. Studies on the synthesis and structure of mitochondrial DNA in cells infected by Rous sarcoma viruses and on the occurrence of intramitochondrial virus-like particles in certain RSV-induced tumor cells. Molec. Cell. Biochem., in press.